Republican National Committee chairman Reince Priebus says there "probably will be more elbows thrown" at the billionaire developer, in an effort to shrink his commanding lead in the crowded field. Speaking on CNN's "State of the Union," Priebus also said to expect candidates to continue dropping out of the race for lack of campaign cash. Former Texas Gov. Rick Perry, Trump's chief GOP critic, withdrew from the race on Friday.

Jeb Bush is mocking Trump. Carly Fiorina, whose face Trump insulted in a Rolling Stone interview, dismissed him as "an entertainer." And Sen. Rand Paul says, "someone has to take him down."

Neurologist Ben Carson, who is in second place, declined Sunday to attack Trump.